People who want to run their own code on their smartphone are probably already a very limited subset of all users.

Yep yep yep. I can see how, as a developer, it would be galling to face artificial barriers to what you can do on a device that you own. But I don't develop for phones, and as a "dumb" user in this case, I'm really happy that someone is trying to keep it secure for me...

If it were possible, many more companies would sidestep the app store like how Fortnite did that with the android play store.

The only reason Fortnite used Apple's app store is because Apple has made it practically impossible to side load apps.

Not only is it possible, it’s trivially easy to sideload apps.

What’s difficult is to distribute commercially, or maliciously without going through Apple.

You don't necessarily need a Mac.